The present invention relates to a combination light diffuser and acoustical treatment and listening room including such fixtures. Air diffusers provide uniform temperature and prevent cold and hot zones. Lighting diffusers uniformly illuminate a room removing optical glare and minimizing light and dark zones. Similarly, a sound diffuser uniformly distributes sound in a room, to provide ambiance, even coverage and removes acoustical glare caused by strong specular reflections. Sound can be controlled by absorption, reflection and diffusion. Sound is attenuated by absorption, redirected by reflection and uniformly distributed by diffusion. While the design of spaces used for speech has typically relied solely on absorption, an optimal design can only be achieved using an appropriate combination of each constituent.
Typical ceiling T-bar lighting units consist of an incandescent, fluorescent or LED light source with a flat or parabolic diffusing element. There are many applications, including classrooms, lecture halls, conference and meeting rooms where a ceiling lighting fixture that also provided sound diffusion or sound absorption would improve communication and speech intelligibility. The present invention solves this problem by teaching a novel approach by incorporating a sound diffusing or absorptive element at the face of the light source to simultaneously diffuse the light providing uniform illumination and sound control.
In the application of sound control acoustic treatments in the design of classrooms, training rooms, conference and meeting rooms, lecture halls, presentation rooms, or essentially any room where high speech intelligibility is required, the complete acoustical palette is considered. Typically the ceiling in a speech room consists of acoustical ceiling tile and lighting fixtures. Why is an absorptive ceiling not conducive to high intelligibility?
As is known, the ear/brain processor can fill in a substantial amount of missing information in music, but requires more detailed information for understanding speech. The speech power is delivered in the vowels (a, e, i, o, u and sometimes y) which are predominantly in the frequency range of 250 Hz to 500 Hz. The speech intelligibility is delivered in the consonants (b, c, d, f, h, j, k, l, m, n, p, q, s, t, v, w), which requires information in the 2,000 Hz to 4,000 Hz frequency range. People who suffer from noise induced hearing loss typically have a 4,000 Hz notch, which causes severe degradation of speech intelligibility.
This raises the question: Why would we want to absorb these important frequencies on the ceilings of speech rooms and prevent them from fusing with the direct sound, thereby making it softer and less intelligible? This appears to be the opposite of what is desirable.
Research has revealed the importance of early reflections and reverberation to intelligibility. There is a difference between hearing speech and understanding it. When early reflections arrive in a temporal window roughly 20-50 ms after the direct sound and roughly between 5 and 15 dB below the level of the direct sound, there is a process called temporal fusion in which the direct sound is fused with the early reflections making it louder and more intelligible. So one important design criterion for small rooms used for speech is to provide early reflections and to not absorb them!
Many of the problems that arise in poorly designed speech rooms stem from a low Signal to Noise Ratio. The signal consists of the direct sound and early reflections (between roughly 20-50 ms). The noise consists of reverberation, occupant noise, exterior noise intrusion and noisy MEP systems. Adults typically require 0 dB signal-to-noise ratios for high speech intelligibility when listening to simple and familiar speech material for short periods of time. An additional 2 dB is needed to compensate for neurological immaturity. An additional 5 dB is required to compensate for sensorineural and conductive hearing losses. An additional 5 dB is required for limited English proficiency and language disorders. An additional 3 dB is required to compensate for the effects of excessive reverberation. These additional requirements for speech rooms total 15 dB over that of normal adults, or a signal-to-noise ratio of +15 dB. Passive acoustics in the architecture can be employed to provide some of this needed gain. Most design approaches only try to reduce the noise and often simultaneously decrease the strength of the signal as well, by using only absorption. The result is no net improvement. Excess reverberation can also corrupt the purity of the speech signal and decrease intelligibility. So it is important to increase the signal, by (1) introducing diffuse ceiling reflection, and (2) decreasing all forms of noise, including reverberation. At the same time, ceiling illumination is also required, but it is often located in locations where acoustical treatments should optimally be positioned. Hence, there is a need for combining sound diffusion and lighting, as well as sound absorption and lighting to reduce the reverberation time. It would be advantageous to place luminous absorptive fixtures around the perimeter of the room, to complement centrally located luminous diffusers. It is with these thoughts in mind that the present invention was developed.